Security system, particularly for valuable documents

ABSTRACT

The invention relates to a security system especially for security documents, wherein a security element is provided in a carrier plane, that under incident light holographically reconstructs a pattern outside the carrier plane, in which concealed information is stored and having a flat transparent verification element which on flat contact with the security element makes the information stored therein visible. The invention further relates to a security element and a verification element for use in the security system and a security document fitted with the security system. The invention additionally relates to an apparatus and a method for reading out the concealed information which is stored holographically in the pattern reconstructed on the security element under incident light.

BACKGROUND OF THE INVENTION

The invention relates to a security system, especially for verifying theauthenticity of security documents, consisting of a security element anda verification element which make concealed information visible by flatcontact one with the other, and corresponding security elements,verification elements and security documents. The invention furtherrelates to methods and apparatus for reading out concealed information.

Documents, certificates, banknotes, identity cards, plastic cards etc.can be reproduced faithfully in detail and colourfast with the aid ofmodern high-resolution colour scanners and using colour laser printersor thermal sublimation printers. As a result of the general availabilityof colour copiers, it has also become substantially easier to producehigh-quality forgeries.

There is thus a need to make documents, identity cards, banknotes,security papers, plastic cards etc. secure against forgery by means ofadditionally applied security features. By means of such securityfeatures it can at least be accomplished that the production of ahigh-quality forgery is substantially more expensive. Water marks, silkthreads, intricate line structures and the use of special papers areknown as such security features. The application of metallised embossedholograms on bank notes, credit cards and Eurocheque cards has alsobecome generally used in the meantime.

WO 98/15418 discloses a self-verifying security document which carriesinformation at one location which is not generally recognisable undernormal examination. At another location on the document there is applieda verification element which by folding the security document can bebrought into register with the security element bearing the concealedinformation so that the concealed information becomes visible. It isdescribed that, for example, text written in microscript in the securityelement is magnified with the aid of an optical lens as verificationelement when the verification element is brought into register with thesecurity element by folding the security document. It is also possiblethat the security element and the verification element are configuredsuch that when the verification element covers the security element,they produce a so-called Moiré pattern. By suitably configuring thepattern contained in the verification element or security element,information in the Moiré pattern can be made visible in this fashion.Finally, both the security element and also the verification element cancomprise a polarisation element. If the alignment of the plane ofpolarisation differs suitably from one region to another, informationcan be made visible in this fashion.

However, with the continually improving copying and forgery techniquesat the present time, there is a risk that such flat elements do notoffer sufficient security against forgery. Thus, for example, it can beexpected that even text applied in microscript can be reproduced using acopier of sufficient resolution. Likewise, the patterns for producing aMoiré pattern can also be reproduced if necessary.

It is thus desirable that the security or verification elements have aneven higher degree of security against forgery so that firstly, securitydocuments can be made even more secure against forgery and theverification of authenticity can be more reliable.

This object is achieved using a security system having the featuresherein, a security element having the features herein, a verificationelement having the features herein, a security document having thefeatures herein, a readout method having the features herein or areadout device having the features herein.

A security system according to the invention comprises a flat securityelement arranged in a carrier plane. The security element comprises ahologram carrier which, under incident light, reconstructs a pattern ina holographic fashion which lies outside the carrier plane. Concealedinformation is stored in this pattern. The security system according tothe invention also comprises an at least partially transparentverification element which on flat contact of the security element underincident light makes it possible to read out the information concealedin the pattern produced holographically by the security element.

On or in an object to be secured, e.g., a security document or banknotethere is thus a security element at one location. This security elementis a hologram carrier. Under the incident light, the hologram containedtherein produces an image or pattern displaced with respect to thedocument to be secured, which can be two-dimensional orthree-dimensional. Concealed information is stored in the pattern. Thisconcealed information, which is now located at some distance from thedocument can be read out using a verification element.

The concealed information is thus not applied directly to the securitydocument as with known security features but is only generated at somedistance from the security document in a holographic fashion. Thehologram of the security element makes forgery significantly moredifficult. In contrast to holograms already used as a security elementso far, the information stored in the holographically generated patternis however, only made visible by the verification element.

In this way very much better protection against forgery is achieved. Inaddition, the information is not identifiable without the verificationelement and thus is not copiable.

In an advantageous development of the security system the securityelement comprises a hologram which produces a phase-modulated patternunder illumination. The concealed information can in this case be storedsuch that the phase of the light in the region of the concealedinformation is different to the phase of the surrounding regions of thepattern. The verification element is then configured such that itconverts this phase modulation into a visible amplitude modulation. Thiscan be achieved in a known fashion, for example, by the phase contrastmethod or the Schlieren method.

In a more advantageous development the verification element alsocomprises a hologram which, under incident light, reconstructs acorresponding pattern which produces an optical light pattern needed toconvert the phase modulation into an amplitude modulation.

Another advantageous development of the security system according to theinvention comprises a security element which is a hologram which underincident light again reconstructs a line pattern outside the carrierplane. The verification element is also a hologram which produces a linepattern in the same plane outside the carrier plane. The line patternsare configured such that a Moiré pattern is formed in the same way as iftwo line patterns actually present at the location of theholographically reconstructed line patterns had been brought intoregister. By suitably configuring the holograms and the line patternsthereby produced, information can be stored in the Moiré pattern whichonly becomes visible when they overlap.

In another advantageous development of the security system according tothe invention, the security element again produces a pattern in aholographic fashion outside the carrier plane under incident light. Thispattern is amplitude-modulated such that it cannot be identified withthe naked eye. The verification element comprises a lens structure whichmakes the amplitude modulation visible to the eye when the verificationelement is superposed on the security element. For example, the lensstructure can be a strip lens structure.

In the development the necessary distance between the object to beimaged by the lens structure, in this case the holographicallyreconstructed pattern of the security element, and the lens structure isachieved by the holographically produced pattern lying outside the lensplane or the contact area between the verification element and thesecurity element. In this fashion a suitable lens structure can be usedfor verification without this having a thickness necessary to producethis distance. For security documents such as banknotes the thicknessshould be kept as small as possible. In this respect, this developmentaccording to the invention offers the possibility of utilising theadvantages of security against forgery using lens structures even onthin security documents.

In another development of the invention, both the security element andthe verification element produce a pattern outside the contact area ofthe verification element and the security element in a holographicfashion under incident light. Both patterns thus produced each carry adifferent part of the concealed information. Only when the verificationelement is brought into register with the security element are the twoparts of the concealed information reconstructed with the patterns underincident light and made identifiable in their entirety.

Another development of the invention comprises a security element whichagain reconstructs in a holographic fashion outside the carrier plane apattern which is polarisation-modulated. The concealed information is inthis case produced such that in the region of the information thepolarisation differs from that in the surrounding region. Theverification element in this development is a polarisation filter withwhich the different polarisations can be made visible in a knownfashion. In this way the concealed information becomes identifiable.Likewise the security element can also produce a light pattern ofconstant polarisation and the concealed information can be stored in apolarisation-modulated verification element.

In a further development of the invention the security element is againconfigured such that it reconstructs an amplitude-modulated patternoutside the carrier plane under incident light. This amplitudemodulation carries the concealed information. The verification elementcomprises a grating structure on a window element. By suitably matchingthe shape of the grating structure and the holographically producedamplitude modulation, a tilting effect can be achieved as a result ofthe holographically produced distance between the grating structure andthe amplitude modulation. Depending on the direction in which thegrating of the verification element is viewed, it is possible to seeunder the lines of the grating structure, for example and theinformation present there becomes visible. On the other hand when theverification grating structure is viewed perpendicularly, theinformation visible between the grating lines of the verificationelement becomes visible. In this way information can be made visibleaccording to the angle of tilt of the superposed elements.

In order to achieve even greater security against forgery, the securityelement can be configured such that under incident light, it produces aholographically generated pattern which, however, does not have aconstant distance from the carrier plane. The verification element musttake this circumstance into account by means of suitably matched localfrequencies. With such a configuration no information is visible in theplane of the security document. The pattern in which the concealedinformation is stored is only produced by holographic reproduction. Thispattern is not in a plane but has a varying distance from the plane ofthe security element. This varying distance can only be compensated withthe aid of the verification element. In addition, the information isadditionally concealed in that it is stored in the holographicallyproduced, non-plane pattern, e.g. is only stored as phase modulation,polarisation modulation or a line pattern to produce a Moiré pattern. Inthis case, the verification element thus has different tasks. Firstly,it equalises the different distance of the holographically producedpattern from the carrier plane. Secondly, it makes visible theinformation concealed in the holographically produced pattern.

The holographically produced pattern which is formed on the securityelement as a result of the incidence of light can have differentdistances from the carrier plane. Especially advantageous however is theorder of magnitude of several 100 μm, more advantageously 100 to 300 μm.In this way a 3D hologram can be produced. Despite the difficultiesinvolved in applying or inserting a hologram onto the rough surface of abanknote, for example, the lack of definition can be kept withintolerable limits for a 3D hologram that produces a pattern at such ashort distance from the carrier plane.

The information stored in the holographically generated pattern, whichappears as a result of light being incident on the security element canbe read out using an external verification element. However, it isespecially advantageous if both the verification element and thesecurity element are applied to one and the same security document. Bysuitably folding the security document, the elements can then be broughtinto register in order to make the concealed information visible. Inthis way, it is possible to have a self-verifying system. With asuitable arrangement of elements on the banknotes, the same effect canalso be achieved by superposing two banknotes in correspondingalignment.

The pattern reconstructed as a result of the incidence of light on thesecurity element can be virtual or real according to the configuration,i.e. it can be imaged on a screen.

A security element according to the invention for use in a securitysystem according to the invention comprises a hologram structure whichreconstructs a pattern with concealed information outside the carrierplane in a holographic fashion under incident light. A verificationelement for use with a security system according to the invention servesto make visible the concealed information which is reconstructed by asecurity element according to the invention outside the carrier plane ofthe security element when light is incident.

The verification element is at least partly transparent. In addition tothe structures which serve to make the concealed information visible,the verification element can also have a further security feature. Forexample, a further hologram structure can be applied which producesanother image which is superposed on the concealed information as abackground.

A security document according to the invention comprises a securityelement according to the invention and/or a verification elementaccording to the invention.

In a method according to the invention for reading out informationconcealed in the pattern reconstructed holographically on the securityelement under incident light, a verification element according to theinvention is brought into register with the security element. If thesecurity element and the verification element are provided on abanknote, for example, it is advantageous if the verification element isbrought into register with the security element by folding the document.In this way, verification is possible without the need for further aids.

The security system according to the invention can be configured suchthat when the verification element and the security element suitablyoverlap, the concealed information is made visible to the naked eyeunder suitably incident light. However, an apparatus according to theinvention can also be provided which makes verification possiblemechanically. Such an apparatus comprises a device which brings thesecurity element into register with a verification element. In thiscase, the verification element can be part of the apparatus or it can beapplied to the object to be verified itself and can be brought intoregister with the security element by mechanical folding. Anillumination device is provided which illuminates the security elementand verification elements brought into register. The concealedinformation thus becomes visible and can be read out with the aid of areadout device. This can, for example, be a brightness detector whichcan detect brightness differences in the concealed information. Finally,the readout device can be a camera which makes it possible to processthe image and evaluate the image of the concealed information.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention according to the invention are explainedwith reference to the appended drawings wherein

FIG. 1 is a schematic view of a security document according to theinvention with a security element according to the invention,

FIG. 2 is a schematic view of a readout device according to a methodaccording to the invention,

FIG. 3 is a schematic view of a mechanical readout process according tothe invention,

FIG. 4 is a schematic side sectional view of an embodiment of a securitydocument according to the invention during the readout process,

FIG. 5 is a schematic side sectional view of a further embodiment of thesecurity document according to the invention during the readout process,

FIG. 6 is a schematic side sectional view of a further embodiment of thesecurity document according to the invention during the readout process,

FIG. 7 is a schematic side sectional view of a further embodiment of thesecurity document according to the invention during the readout process,

FIG. 8 is a schematic side sectional view of a further embodiment of thesecurity document according to the invention during the readout process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a security document 1, e.g. a banknote with a verificationelement 3 and a security element 5. In the example shown theverification element is shown hatched. The security element 5 comprisesa hologram carrier. According to one embodiment, under incident lightthis hologram carrier produces a pattern outside the plane of thedocument 1, e.g. the banknote. The pattern thus produced holographicallyis advantageously at a distance 7 of 100to 300 μm from the surface ofthe banknote 1. The reference numbers 1, 3, 5, 7, and 9 are usedgenerally in the following for various embodiments.

In an embodiment in which the verification element 3 carries a linegrating, under incident light the security element 5 produces aholographic pattern that is also modulated in a stripe fashion. If averification element 3 is brought into register with the securityelement 5, the line grating of the verification element is at a distancefrom the holographically produced pattern. In this fashion, by tilting,for example, the region below the line grating can be made visible or byviewing in the perpendicular direction, the region between the lightgrating of the verification element 3. In this fashion tilting effectscan be produced which are otherwise only visible in the presence of anactual spacing between the grating pattern and the image plane.

In FIG. 7 such an embodiment is shown schematically in a side sectionalview. Shown is a folded banknote 1 where the verification element 403and security element 5, 405 have been brought into register. This is theposition during the readout process. In this description the term“readout” is used generally for the verifying, whether this is with thenaked eye or mechanically.

When light is suitably incident, a holographically produced pattern 400reconstructs from the hologram of the security element 5, 405 at thedistance 7 from the plane of contact 9. The verification element istransparent and provided, for example, with a printed-on stripe pattern.As a result of the distance 7, the region of the holographicallyproduced pattern 400 which is visible through the stripe pattern of theverification element 3, 403 depends on the direction of viewing onto thesecurity element 5, 405. Depending on the viewing direction, forexample, the region below the stripe pattern 3, 403 can be visible orthe region between the stripes of the verification element 3, 403.

As also in FIGS. 4, 5, 6 and 8, the region in which the verificationelement and the security element are located is indicated by shortperpendicular lines on the banknote 1. Naturally these are not objectivefeatures. In addition, FIGS. 4 to 8 should not be seen as true to scale.Especially, for example, the distance 7 is very much smaller. Theverification element and the security element lie directly one on top ofthe other and are preferably each no thicker than the banknote 1.

The security element 5 which is visible in FIG. 1 can also be a hologramcarrier which produces a phase-modulated pattern outside the plane ofthe banknote 1 under incident light. In this case, the verificationelement 3 is an element that converts this phase modulation intoamplitude modulation. For example, if this phase modulation is in theform of the letters OK, by superposing the verification element 3 withthe security element 5, as shown in FIG. 2, the concealed information“OK” 6 becomes visible to the eye 8.

In another embodiment shown in side view in FIG. 5, the security element5, 205 produces a line pattern 200 outside the plane of the banknote 1under incident light. The verification element 3, 203 also produces aline pattern under incident light in the same plane outside the banknote1 if the verification element 3, 203 and the security element 5, 205 aresuperposed. The line patterns are adjusted such that a Moiré pattern isobtained, as is known for the superposition of actual line patterns.Information can be stored in this Moiré pattern by means of a suitablearrangement of the holographically produced lines so that the letters“OK”, for example again become identifiable.

Finally, the security element 5, 105 can also produce a pattern 100outside the plane of the banknote 1 which is made visible with the aidof a lens structure 102 in the verification element 3, 103, e.g. bymagnification, see FIG. 4. For this purpose the lens structure must havea certain distance 7 from the pattern to be imaged which is obtainedaccording to the invention by the holographic reconstruction of thepattern 100. The lens structure 102 does not need to have a certainthickness, as is usually the case, to produce this distance from theobject to be imaged. For example, a lenticular lens structure ispossible.

Another simple embodiment comprises a security element 5 which underincident light reconstructs a holographically produced pattern outsidethe plane of the banknote 1, which only carries some of the informationwhich by itself is not expressive. The verification element 3 comprisesa comparable holographic structure which reconstructs a holographicallyproduced pattern in the same plane outside the banknote 1, whichrepresents the remainder of the information. If the verification elementis now brought into register with the security element and exposed tolight, both parts of the concealed information become visible and can beread out together.

For example, the part information produced in a holographic fashion byilluminating the security element 5 can comprise parts of the letters Oand K which by themselves alone are not recognisable as such. Theremaining parts of the letters O and K are produced by illuminating theverification element holographically at the same location when the twoelements come to lie one on top of the other. In this fashion thecomplete image OK becomes recognisable.

In another embodiment of the side view in FIG. 6, there is, for example,a security element 5, 305 which holographically produces a pattern 300outside the plane 9 of the banknote 1 which has different polarisationin different regions. Whereas, for example, most of the holographicallyreconstructed pattern 300 has a vertical polarisation, the polarisationin the region of the letters O and K is horizontal. The verificationelement 3, 303 is a polarisation filter which is vertically polarised.In this fashion the horizontally polarised light from the regions of theholographically produced pattern, corresponding to the letters O and K,cannot pass through the verification element 3, 303 so that these appearblack.

The holographically produced distance 7 between the reconstructedpattern of the security element makes forgery difficult. The usualdirect storage of information on the banknote is easier to forge than ahologram which exhibits corresponding information in a displaced plane.In addition, the information is such that it can only be read out withthe aid of the verification element. Without such a verification elementthe holographically stored information is unrecognisable. Even highersecurity from forgery can be achieved if the holographically producedpattern 505 does not have a constant distance 7 from the banknote 1 but,for example, reconstructs in a wavy surface or in a stepped surface, asshown schematically in FIG. 8. Again the waviness is very much smallerthan shown. In such an embodiment the verification element 3, 503 isconfigured such that it takes account of this non-constant distancewherein this can be achieved by a suitable local frequency of theverification element.

The hologram structures required for the above embodiments can beproduced optically in the conventional fashion or they can becomputer-generated. They can naturally be provided at differentlocations or even in plurality on the banknote. Likewise, an arrangementin two opposite corners of the banknote is feasible for example. Thesecurity element can produce both a virtual and a real image which canbe captured on a screen.

The verification element 3 is at least partly transparent. Thus, lightcan pass through the verification element onto the security element andmake the holographic pattern stored therein visible behind the banknote1. Examining this pattern through the verification element makes theconcealed information visible.

In addition, another security feature can be provided on theverification element itself, e.g. a further hologram structure whichcauses another optical effect in order to further increase the securityagainst forgery. Naturally, the transparency of the verification elementmust remain sufficient so that the concealed information can still beread out. FIG. 2 shows the readout process. Viewer 8 sees the foldedbanknote 1. The verification element 3 lying on the security element 5makes visible the information concealed in the pattern generatedholographically by the security element 5.

FIG. 3 is a schematic view of a mechanical arrangement for reading outthe security system. In a fashion not shown the banknote 1 is foldedmechanically so that the verification element 3 and the security element5 come to lie one on top of the other. In a transport device again notshown, the banknote thus folded is brought into the beam path of anillumination device 10 with a light direction 12. The light beam 12passes through the verification element 3 onto the security element 5that is not visible in FIG. 3. There the pattern is producedholographically outside the banknote 1 by the security element 5. Theholographically produced pattern is recorded by the verification element3, that is at least partly transparent, with the aid of the camera 14,e.g. a CCD camera, in the direction 13. The verification element 3thereby makes recognisable the concealed information visible in theholographically produced pattern. The image thus produced with thevisible concealed information is fed from the camera 14 to a computerunit 16, for example. Here the image can be evaluated using known imageprocessing methods, e.g. a comparison with expected images in order toverify authenticity.

With a suitable configuration of the security element 5, the lightsource 10 can also be arranged behind the folded banknote 1.

In another embodiment of an apparatus for readout according to theinvention which is not shown here the verification element is not fixedto the banknote but in the machine itself and the banknote 1 is movedpast with the security element 5 thereon.

The security system according to the invention thus offers the advantagethat the concealed information is stored in a pattern that does not liein the plane of the banknote or the security document 1. Instead ofthis, the pattern is produced holographically outside the securitydocument 1. This makes forgery significantly more difficult. Inaddition, such holographic displacement of the pattern with theconcealed information makes verification possible using elements whichnormally must have a certain distance from the pattern with theconcealed information, e.g., lenticular lens structures or line gratingswith a tilting effect. No increased thickness is needed for this purposein the invention since the distance is produced holographically.

1. Security system for a security document, with a flat security elementin a carrier plane that under incident light holographicallyreconstructs outside the carrier plane a pattern in which concealedinformation is stored, and with a flat at least partly transparentverification element which on flat contact with the security elementmakes the information stored therein readable, wherein the securityelement comprises a first hologram carrier which reconstructs outsidethe carrier plane a polarization modulated pattern whose polarization inthe region of the concealed information differs from that in theremaining region and the verification element comprises a polarizationelement.
 2. Security system according to claim 1, wherein the securityelement and the verification element are arranged on the same securitydocument.
 3. Security system according to claim 1, wherein the distanceof the pattern reconstructed by the incidence of light on the securityelement from the carrier plane is in the range of several 100 μm. 4.Security system according to claim 3, wherein the distance is in therange of 100 to 300 microns.
 5. Security system according to claim 1,wherein the verification element and the security element are applied orinserted onto or in an object such that they can be brought into flatcontact by folding the object.
 6. Security system according to claim 1,wherein the security element is configured such that the patternreconstructed by the incident light is a real image.
 7. Security systemaccording to claim 1, wherein the verification element is fitted with anadditional security feature.